1. Field of the Invention
The present invention relates to an apparatus and method for removing interference signals using a selective frequency phase converter (or phase shifter) and, more particularly, to an apparatus for effectively removing interference signals by selectively phase-converting a signal of a particular frequency band by using simple hardware.
2. Description of the Related Art
An RF signal received in a wireline/wireless communication system includes signals from unnecessary frequency bands as well as signals from the necessary particular frequency band, and such undesired and unnecessary signals from other frequency bands are known as interference signals. Because most interference signals include signals generated by other systems, they have considerably powerful signal power strength, making the operation of electronic parts of a receiver system enter a saturated state, which can result in degradation of receiver performance. Thus, in order to ensure the stable operation of a receiver system, the strength of the interference signals must be attenuated to below a certain level in a front stage of a receiver. In addition, as an ideal communication system is supposed to only receive a signal of a particular required band, the removal of interference signals is closely connected with the performance of the communications system.
The related art method for removing interference signals includes a method of using a band pass filter, a method of using a notch filter, a feed-forward method, and various others.
The method of using a band pass filter allows a received signal to pass through a band pass filter having a pass band including a particular required frequency band. In this method, signal loss occurs to some extent even in the pass band, due to the non-ideal characteristics of the band pass filter, leading to an attenuation of even the signals of the particular required frequency band. In addition, in order to use the band pass filter, an external element must be mounted in the system, increasing the size of the system.
The method of using a notch filter allows a received signal to pass through a notch filter that removes signals of a certain range of frequency band. This method is effective for removing interference signals present in a narrow frequency band, but has difficulty in removing interference signals distributed across a wide frequency band.
The feed-forward method is where a received signal is first down-converted, such that its particular required frequency band is positioned at a baseband, namely, in the vicinity of DC, and allowed to pass through a high pass filter to remove a signal of particular required frequency band. The resultant signal's phase is then converted (i.e., shifted) by 180°, which is then up-converted so as to be added to the originally received signal, thus removing interference signals. This method is advantageous in that signal loss is minimal and interference signals across a wide frequency band can be effectively removed, however, the hardware configuration is complicated due to the fact that a down-converter and up-converter as well as a high pass filter must necessarily be used.